Effect Of Pulsed Ventilation On Harmful Gases Control And Wastewater Quality Changes In Sewer

Municipal sewer pipes are important public infrastructure of a city.The hydrogen sulfide（H₂S）,methane（CH₄）,carbon monoxide（CO）and other harmful gases produced in sewer can cause serious problems to sewer operation.The natural pulsed ventilation system is a new method to control harmful gases production in sewer.In this system,the building drainage pipe is linked to the municipal sewer pipe,directly.Then the air entrained by the building drainage pipe can change the anaerobic environment and reduce the production of harmful gases in gravity sewer pipe.To determine the effect of pulsed ventilation on harmful gases control and wastewater quality changes in sewer,a laboratory reactor system which simulated a real gravity sewer pipe was set up.The concentration of harmful gases,the wastewater quality parameters and microbial community composition were tested.The results showed that:（1）The pulsed ventilation could effectively improve the oxygen（O₂）concentration in the gas space of gravity sewer pipe and improve the oxidation-reduction potential（ORP）value of wastewater.Under the pulsed ventilation condition,the O₂ concentration in the gas phase space of sewer pipe could reach 6.5%,which was 46.55%higher than the sewer pipe without ventilation.After each ventilation event,the ORP value increased from-289 m V to-252 m V pulsed within 1～4 h,with an increase of 12.72%.This may change the anaerobic environment and increase the chemical oxidation of sulfide in sewer.（2）The pulsed ventilation could effectively inhibit the production of H₂S and CO in gravity sewer and postpone the accumulation of CH₄.Compared with the sewer pipe without ventilation,the concentration of total sulfide in the upstream and downstream sewer pipe reduced by 39.08%and 58.74%,respectively.And the concentration of CO in the upstream and downstream sewer pipe reduced by 60.56%and 72.51%,the concentration of CH₄ reduced by 42.29%and 35.70%,respectively.The pulsed ventilation has obvious effect on harmful gases control in gravity sewer pipe.（3）The pulsed ventilation could accelerate the transformation of pollutants in sewer pipe.Under the pulsed ventilation condition,the SCOD concentration in the effluent wastewater of sewer pipe reduced by 19.45%compared with the sewer pipe without ventilation.The total nitrogen concentration reduced by 3.86%,ammonia nitrogen concentration reduced by 4.17%and nitrate nitrogen concentration reduced by14.58%.The total phosphorus concentration reduced by 3.71%.The sewer pipe could be regarded as a reactor for biological reaction of wastewater.And the low concentration of SCOD may be conducive to the harmful gases control.（4）The pulsed ventilation could improve the microbial diversity and change the microbial community composition of biofilms in sewer pipe.The pulsed ventilation increased the proportion of Gammaproteobacteria and Cloacimonadia,and inhibited the growth of anaerobic microorganisms such as Aminomonas,Trichococcus and Lactococcus.This may facilitate the carbon,nitrogen and phosphorus pollutants transformation in sewer pipe with pulsed ventilation.The pulsed ventilation inhibited the proliferation of sulfate-reducing bacteria（SRB）such as Desulfovibrio and stimulated the proliferation of sufur-oxidizing bacteria（SOB）such as Sulfurospirillum to reduced the production of H₂S.Furthermore,the pulsed ventilation inhibited the proliferation of Methanobrevibacter and Methanospirillum,stimulated the proliferation of Methanobacterium and Methanosarcina.The changed composition of methanogenic archaea（MA）under pulsed ventilation condition was related to the reduction of CH₄ in sewer pipe.